1. Field of the Invention
The present invention is broadly concerned with improved methods for treating metallic surfaces with epoxy/curing agent anti-corrosion systems. More particularly, the invention is concerned with such methods wherein the respective epoxy and curing agent system components are separately and sequentially contacted with the metal surfaces of oil or gas recovery or conveying equipment. The invention is particularly advantageous in that it permits long gas pipelines or deep producing wells to be successfully treated with anti-corrosion systems.
2. Description of the Prior Art
It is well known that oil and gas wells are subject to extensive corrosion. Downhole equipment such as sucker rods, pump rods, tubing and casing are generally made of mild steel which is adversely affected by the production fluid of the well. The often high temperatures and acidic nature of the production fluids and formation waters magnifies these corrosion problems. Additionally, oil or gas-conveying pipelines are also prone to corrosion.
A variety of anti-corrosion systems have been described in the past. Many corrosion inhibitors are aqueous dispersions containing a variety of components, e.g., 2-mercaptobenzothiozole, benzotriozole, tolyltriozole, phosphates, polyphosphates, organic soluble polymers, silicates, dithiocarbamates, nitrites, oxazoles, imidazoles, imidazolines, lignands, lignosulfates, tannins, phosphoric acid esters and boric acid esters. Many of these inhibitors are very prone to freezing during cold weather, making them very difficult to handle and maintain. Moreover, the useful life of many prior anti-corrosion treatments is very short, e.g., a week or less.
U.S. Pat. Nos. 5,936,059 and 5,945,164 describe highly useful anti-corrosion systems and methods particularly suited for oil and gas recovery and conveying equipment. The systems of the invention include an epoxy component as well as an amine curing agent component, which are either mixed together at the introduction site, or are simultaneously injected into a well or pipeline. A problem has arisen, however, when extremely long pipelines or deep wells require treatment. In such cases, the admixed epoxy and curing agent components tend to prematurely cure prior to application along the full length of the well or pipeline, meaning that certain portions of the equipment are not successfully treated. See also U.S. Pat. No. 4,526,813.